


Light Me Up

by Daiako (Achrya)



Category: Fate/Grand Order
Genre: Alpha/Beta/Omega Dynamics, Body Modification, Explicit Sexual Content, M/M, Mating Cycles/In Heat, Plot What Plot/Porn Without Plot, Porn with Feelings
Language: English
Status: In-Progress
Published: 2019-02-11
Updated: 2019-03-16
Packaged: 2019-10-26 01:32:12
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 7,861
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/17736485
Author URL: https://archiveofourown.org/users/Achrya/pseuds/Daiako
Summary: Ritsuka wasn't a mage, until he had to be, and as much as he wants to be able to help there are some limitations. He's willing to do whatever it takes to surpass those limits, but he couldn't begin to imagine what would be required of him, and what changes it might cause, to do so...AKA Ritsuka has to be 'intimate' with some of his servants to get around his magical circuits burning out.





	1. Good Boys Go to Heaven

**Author's Note:**

> Listen, this is just self indulgent porn that will follow my own game regarding what servants appear when and where. It's just for fun, so don't take it or the way I abuse canon seriously.

“I’m going to look ahead.” Archer didn’t wait for a response from Ritsuka before turning and hopping over a destroyed wall and darting away into the inky shadows that surrounded them. Only the flickering of flames, burning just as strongly as when they’d arrived hours ago, broke up the darkness. Not that the erie twisting shapes and glow the fires cast over them, or the constant crackles and hiss that filled the air, were much better. 

Ritsuka leaned back against the crumbling wall the servant had so easily scaled and wiped at the sweat beading from his brow, teeth gritted against the pounding in his skull. Even though he wasn’t directly fighting the skeletal monsters roaming Fuyuki his body was sweaty, enough that his shirt was clinging to his skin and his hair stuck to his skull, and aching like he had been. He felt run down, sore all over, and his head felt like it was full of rocks tumbling around each other, crashing and grinding. The throbbing behind his eyes was near unbearable, and the dull ringing in his ears made it even worse. 

Even swallowing hurt; it made the crushing pressure in his head grow, pushing out against his skull from the inside. He closed his eyes, groaning quietly, and put a hand to his forehead. This was not what he’d expected when he’d woken up today, at all. All of this, the explosion, ray shifting, Mash now being a demi-servant, summoning Archer, and all the fighting, it barely seemed believable to him. He half expected to wake up at any moment, back in his apartment, with everything from the moment he saw that flyer at the train station until now as part of some crazy dream. 

Especially the summoning part. To think that he’d managed to call a Heroic Spirit and make a contract with him, a sort of magic he hadn’t even realized was real or possible for someone like him. Even though he’d been tired since, and during he’d felt like something was being torn from deep inside of him, he couldn’t help but feel a little proud of himself. 

“Fujimaru? Are you listening?” Ritsuka cracked open an eye to squint at a frowning Olga Marie. Her eyes darted up, down, and back again before she sighed. “What’s wrong with you? Are you hurt? If somethings wrong you need to let us know, you’re the only-” 

“I’m not hurt!” Ritsuka blurted, straightening up. Mashu was standing just behind Olga Marie, leaning against her shield, eyes wide and troubled as she listened. She stood up a little straighter at the mention of him being hurt and that was enough to force back the worse of his pain for a moment. “I’m not. I’m just...tired.” 

Very tired. He had never been so exhausted in all his life, even though all he’d been doing was walking and shouting orders for the most part. Who would have expected such a thing to be so tiring? He rubbed at the back of his neck and smiled weakly at the demi-servants skeptical look.

“Really. None of our enemies go anywhere near me.” 

“You should rest, Senpai.” Mashu said, eyes scanning him carefully, as if searching for any sign that he wasn’t telling the truth. “And eat. We have more dried fruit, don’t we?” 

Olga Marie frowned. “Well, yes but-” 

Mashu hefted her shield up.  “We should head back to the camp then. It’s safer there.” 

Olga Marie’s frown deepened. “We shouldn’t waste time we don’t have! We need to find and correct the singularity.” 

Ritsuka took a step forward. He wanted to stop the argument he could feel brewing between the women; Olga Marie’s face was hard and determined but Mashu’s body was tensed and her mouth an unhappy line. Funny, he wouldn’t have thought Mashu was the type to defy an order, and yet she seemed ready to do so now, on his behalf. But Olga Marie was right, they needed to fix this anomaly and set things right as soon as possible, and then get back to Chaldea so a real Magus and Master could take over and save the future. 

He was, after all, just a normal person meant to fill the ranks. He wasn’t cut out for this kind of thing, summoning servants and giving orders in life or death battles with the fate of the world on his shoulders, and he was sure they could all tell. The sooner this was all done the better; he would just have to keep going no matter how badly he was feeling. He would just- 

The world shifted, leapt up past his face then tilted wildly. His stomach dropped and all at once he could no longer feel anything but a searing pain screaming along his nerve endings. He felt like he was on fire, or maybe had become fire. He noticed the ground rushing towards him fast and realized dimly that he was falling towards the cracked, pitted stretch of destroyed pavement they’d been traveling along. He winced, bracing himself for the impact when his arms refused to lift in his defense (they were numb, heavy as lead, couldn’t do more than twitch with pain at his sides), and shut his eyes tight. 

Maire Olga and Mashu’s cries of alarm echoed in his ears. 

The expected sting of meeting earth never came. Instead there was a jolt at his waist as he hit something that immediately curled and tightened around him. He felt himself being hauled back roughly against a firm surface, held up as another weight settled on his shoulder and held tight. A warm, firm, surface that was slowly rising and falling against his back. He blinked a few times, clearing stars and a wave of neausiating dizziness away, then tilted his head back stare at the pensive face of Archer. Ritsuka blinked again. 

Some of the fire under his skin receded, the burn banking back to a tolerable level. The dizziness faded. 

“I thought you were scouting ahead?” 

Archer’s expression could only be called ‘unimpressed’. “I wouldn’t be much of a servant if I couldn’t tell when my master needed me.” 

“What’s wrong with him?” Olga Marie asked from closer than he recalled her being, so close she could have reached out and touched him. She looked like she wanted to, bottom lip catching between her teeth as her eyes flicked up and down his body and her hands flexed open and closed at her sides. “Can he keep going?” 

“Not like this.” Archer shook his head. 

A soft staticky crackled announced Dr. Roman’s ‘presence’ a moment before the man’s voice filled the air. “I was afraid this might happen.”

“What might happen?”

“I believe summoning and contracting with Archer has caused some backlash on Fujimaru’s body.” Dr. Roman spoke unusually slow, seemingly picking his words carefully. “Fujimaru isn’t a ‘real’ master, and the contract with Mashu forced his magical circuits to come to life, something that is already painful in any case, but luckily she’s a demi-servant and doesn’t demand much from him mana wise, so it likely wasn’t that bad.” Dr. Roman paused, inhaling audibly. 

Olga Marie’s eye twitched. “But?”

“Archer however is a full servant; the mana requirements of the contract wouldn’t be much for a trained Magus but for Fujimaru it’s placing a lot of demands on circuits that were essentially dead before today.” Roman breathed out then, quietly, added. “It may have been too soon to summon a servant. I shouldn’t have suggested it.”

Ritsuka looked down at his feet, face warming up. “We needed Archer’s help. I’m the one who-” 

“I know something that will help.” Archer cut in smoothly; the hand on Ritsuka’s shoulder squeezed gently, a contrast from the servant’s firm tone. “I’ve seen this happen to someone before.”

“You have?” Olga Marie’s eyebrows lifted. “That’s lucky. ...well, what are you waiting for? Get on with it, we don’t have forever.” 

Archer shifted slightly at Ritsuka’s back; he could feel the hesitation in the servant. “I...we’ll need to be alone, for a time.” 

“Alone.” Olga Marie deadpanned. Mashu was already shaking her head in refusal, the stubborn expression back on her face. “Absolutely not. We should see this solution of yours, in case a similar situation should arise-”   

“If that happens I’ll take care of it then.” Archer leaned forward over Ritsuka as the arm around his waist tightened. Ritsuka realized for the first time that he was still in the Servant’s arms, resting back against his body, allowing himself to be held so...intimately, without a single complaint or even noticing. And, it seemed, wasn’t going to be going anywhere anytime soon if how tightly Archer was holding on to him was anything to go by. “You need me to do this, unless you have days to wait for the burned circuits to heal naturally?” 

Olga Marie’s eyes slide to the side. Archer seemed to take it was a win. “Then you aren’t in a position to argue with my methods. Leave my master to me, take Mashu with you back to the camp, to protect you, and wait for us. The doctor can return to what he was doing before.”

“Oh.” Dr. Roman sounded disappointed. “Well. I suppose…”  

Neither Mashu nor Olga Marie looked happy with the declaration. Ritsuka cleared his throat and, even all eyes were on him, forced himself to smile. “It’s okay. Archer will help me and then we’ll get back to fixing things.” 

At least he assumed that’s what would happen. He didn’t know what the servant needed to do that required them to be alone, but he trusted Archer (He was supposed to trust the servants, wasn’t it? Wasn’t that the point of summoning them and making the contracts?), and anything that helped him feel less like he was going to burst into flames at anymore moment was worth doing in his opinion.

“If you’re sure, Senpai.” Mashu said quietly, gaze averted. 

He nodded. “I am.” 

Olga Marie scoffed then, with a toss of her hair, turned away from them. “So be it. Don’t take too long, there’s still a lot of ground to cover.” 

That said she stalked up, head held high and arms crossed over her chest, with a still uncertain Mashu behind her. The demi-servant glanced back no less than a half dozen times before she and Olga Marie finally rounded a corner and disappeared from sight. Archer let out a gusty breath. 

“That girl reminds me of someone I knew, once.” There was laughter in the servants voice but also something fond. Ritsuka tilted his head back to look up at Archer again, noting the small soft smile and far away look in his eyes. 

It must have been someone he cared about. 

“You’ll want to sit down-against the wall should work. Here.” 

Ritsuka was lifted up, in spite of sputtering out a protest at being swept up into the servant’s arms like he was a child or couldn’t walk on his own. Yes, he’d almost fallen over but he felt better now and this was too embarrassing for words! He might not have been a real mage but he could move the few steps back to the shattered wall without help! Archer ignored him, not saying another word until he’d carefully set Ritsuka up on the broken wall, just high enough off the ground that his feet dangled above the strewn bits of rubble. 

He expected Archer to move back, and to stop touching him, but the servant stayed just in front of him, arms slipping away from under his knees and around his waist so his hands could settle instead on Ritsuka’s thighs. Ritsuka swallowed, another hot flush spreading over his face; Archer grinned at him. 

“Ah. So. How does this work?” 

“I could just reinforce your circuits, to make them stronger while your body becomes more used to them.” Archer said, thumbs rubbing back and forth over Ritsuka’s covered thighs. “I can stay here, and do what I need, without taking mana from my master for a time, so as long as you didn’t summon or contract anyone else there wouldn’t be a problem. But,” 

Of course there would be a But. It had sounded far too easy and painless to be true. 

“If you need to make another contract we’ll be back where we started. There’s a second way, if you’re willing.” Archer looked skyward, lips quirking upwards. “Physical contact can be a...direct way, of letting mana flow between us. The more physical contact, the more direct the flow. I can teach you to transfer enough to ‘fill up’ a servant, and then close yourself off for a time, until you have a better handle on things.” 

Ritsuka squinted up at the servant then down at the hands on him. “Oh! That’s why- Okay. Do we just need to be touching, like this?” He did feel better now, didn’t he? Had since Archer had caught him, so maybe- 

Archer huffed out a laugh and shook his head. “No, this isn’t enough; it would take hours to take in enough to heal and replenish after a battle this way. It’s going to have to be more than this, to fill up reserves in a short burst.” 

Of course. Again it would have been too easy if all it had taken was a little touching, wouldn’t it? Still, he would do whatever was needed of him to make up for what he was lacking as a mage. “What will work?” 

Dark amber eyes stared at him, thoughtful for a moment then one of Archer’s hands lifted to cup his face. The servant leaned in, tilted Ritsuka’s head up and back, then...stopped, eyebrows lifting in silent question. Ritsuka swallowed again, heart jumping, thumping hard against his ribcage. Ritsuka looked down, to the side, quickly questioned every choice he’d ever made in life that had brought him to this moment of an actual heroic spirit asking permission to kiss him, and nodded hesitantly. 

It was, he reminded himself when warm lips touched his own, for the sake of the world. It was not, he assured himself when Archer’s lips moved against his own, slotted with his mouth just right to nip at him lightly, because Archer was maybe kind of attractive. It had nothing to do with the guilty thrill he felt when he was encouraged him to part his lips with a swipe of tongue or the was way his stomach twisted when Archer’s tongue slid against his own. 

Strictly world saving business. 

Archer’s hand on his face radiated a soothing warmth. 

His headache was a distant echo of the icepick pain that had settled into his skull after the summoning when they broke apart. Another kiss, wetter, more demanding as Archer’s tongue flicked against the top of his mouth, curled against his, draw back to once again put teeth to his lips and draw it into his mouth, and Ritsuka was gasping when it ended, lungs burning for air, and yet he unconsciously followed the other’s mouth, caught it for a quick peck before a hand on his chest pressed him back. 

“Hold on,” Archer murmured against his mouth. “Another time, if you want, but we have to do this now?” 

‘What’s this?’ was on the tip of his tongue, and was choked on a second later when the servant dropped gracefully down to his knees and reached for Ritsuka’s belt. He yelped, throwing his hands out to stop him. “What are you doing.” 

Archer looked up at him blandly. “If you’re about to tell me you don’t know what a blow job is-”

“Of course I know!” Ritsuka shouted then, looking around wildly, lowered his voice. “I...know. But why are you...doing that?” 

“Fluid transfer.” He said it like it should have been obvious then, when Ritsuka continued to stare back in bewilderment, rolled his eyes. “It’s the most direct method of mana transfer. ...second most direct, but we aren’t in a place for the most direct and I don’t have any- you. Just sit there, Master. Trust me.” 

Ritsuka bit down on his lip hard, focusing on the sting to stop his hands from shaking, and to keep himself grounded. He moved his hands away, gripped the uneven edge of the wall beneath him, and nodded again. Trust. He could trust and it wasn’t like it was going to hurt or anything. He’d never imagined his first time having sex anything like this but he could do this. He would endure it. 

…

Endure might not have been the right word. 

Archer moved quick, got his belt open and zipper down lightning fast, and slipped his hand down into his boxers before Ritsuka could second guess himself. His hand was big, hot, and felt nothing like his own as it completely encircled his length. A few stuff tugs in the confines of his pants and the twisting heat seeped back into Ritsuka’s stomach and he was, once again, panting for air. He squirmed as he grew hard in the servant’s hand. Archer’s thumb found the crown of his cock, pushed back the foreskin and moved over the slit, and Ritsuka bucked up into his grip, a strangled gasp dropping from his lips. 

Archer smirked at him and, without the rhythm of his strokes faltering, used his free hand to tug Ritsuka’s pants and boxers down. Ritsuka tried to help, hips lifting (or maybe he was just chasing Archer’s skilled hand), but he already felt dizzy, weak, under the servant’s touch. 

Cool air hitting heated skin was a shock but was nothing compared to the damp heat of Archer’s mouth and tongue. He licked at the tip of his cock, swirled his tongue around it as saliva dripped from his mouth and his eyes slipped to half-lidded. Another lick, the flat of the servant’s tongue tasting him from tip to root and back again, coating him in spit. His hand started to move again, friction eased by Archer’s spit; Ritsuka’s toes curled in his shoes and his legs shook, moved further apart without him thinking to do it. 

Archer laughed again, flashed him a heated look, and then Ritsuka was slamming his eyes shut and scabbling at the broken stone beneath him with his nails as the servant’s mouth surrounded him. Archer’s mouth was hot, so hot, was it slid down half way down his cock, tongue dragging along the underside, and the suction around him was...Ritsuka didn’t know how to describe it, except for amazing. Better than anything he’d ever felt before. 

Had he felt like he might die less than hour before? It felt so distant now in comparison to the silken texture of Archer’s mouth, to the rise and fall as the servant began to move back and forth over him, down to where his hand was still pumping and twisting deliciously. It seemed silly now, because he was positive this was going to be what actually killed him. Archer’s hand was so different from his mouth, was calloused and rough and moving fast in comparison to the soft blistering heat and unhurried way Archer was sucking him. He went down to meet his hand then pulled back slowly, curled his tongue against him, lingered with just the head on it before reversing back, and made obscene slurping noises the whole time. Down again, a bit further, and the head of Ritsuka’s cock was pressing against something spongy, pushing into a tighter space. 

He clutched at the servant, grabbed soft hair and made a noise he never would have imagined from himself, low and almost wounded, when he was sucked in deeper and Archer’s throat tightened around him. The servant hummed and Ritsuka moaned again, pulled at his hair and felt his eyes start to burn. 

He could tell things were going to be over embarrassingly quick. 

Archer pulled off his cock with a wet pop, and his hand slide up higher to compensate.  Ritsuka cracked open a teary eye in time to watch the servant lap at his slit again, chasing away drops of precum oozing from the tip before turning his attention to just under the head, pressing his tongue up against the sensitive spot there. His lips were puffy and wet with spit and the way his mouth was open, tongue out as he licked, hit Ritsuka like a physical blow. His chest hurt watching him, constricted tighter and tighter with each wet glide of Archer’s hand and swipe of his tongue. 

With one last lick Archer’s mouth closed over him again and the servant’s hand moved to press against Ritsuka’s hip. Archer swopped down, all the way to the root, and then swallowed around him with a muffled gulp. Everything went tight, vibrated and jumped around him, relaxed and then tightened again. 

“Oh! Ngh, Ar-Archer!” He ground the words out through clenched teeth, the warning he wanted to get out not coming out nearly fast enough. He spilled into the spirit’s mouth, down his throat, with a shout; Archer swallowed again, long deep pulls as he took it all in. 

Ritsuka all but doubled over the spirit, still clutching his head, as his orgasm stretched on and his release was milked from him until he was completely spent. Archer finally pulled away, let his cock fall from his mouth wetly as his hands lifted to hold onto Ritsuka. He was pushed up gently, held in place to keep him from tipping off the wall or falling over. He watched dimly as Archer licked his lips, a small satisfied smile on his lips. 

“Feel better?” 

“...uh?” Ritsuka offered, brain unwilling to offer up anymore. Archer nodded and patted his shoulder. 

“Good.” He kept one hand on Ritsuka and the other went between them to take hold of his cock, sticky wet and sensitive enough that he jumped at the contact, to tuck him away. “And you can call me Emiya. Your my master, and should have my true name.” 

Ritsuka nodded absently, more than willing to go along with whatever his servant had to say. 

\----

“This is Caster.” Olga Marie gestured to the hooded man standing at her side. “He saved us from another servant while you were busy,” Ritsuka knew he was blushing, could feel it creeping over his skin. “His original master is gone but he has the same goal as us, so I think you should contract with him.” 

Ritsuka looked at Caster then whipped his head around to look at Emiya. Emiya shrugged and waved a lazy hand. “Don’t look at me, you’re in charge here.” 

“Would I have to...um.” 

Emiya shrugged gain. “Unless you want to burn your magical circuits again.” 

He looked at Caster again. Caster smirked at him and lifted an eyebrow. “Oh? What exactly are we going to have to do to form a contract then?”  

Ritsuka’s face burned hotter.

  
  



	2. But Bad Boys Bring Heaven to You

 

“You did what?! With your servant?” Olga Marie shrieked, steadfastly ignoring that they were not in a place for screaming, lest they bring more enemies down on their heads, in favor of grabbing Ritsuka by the collar and dragging him uncomfortably close. Her face was flushed a deep red and her eyes were wild as her cheeks puffed out, like she was getting ready to shout again. 

A tanned hand came between them to grasp Olga Marie by the wrist. Her eyes darted up, flush on her cheeks deepening and spreading, and her mouth twisted into a frown. 

“I’m only going to ask you to let go of my master once.” Emiya said, the seriousness of his voice  not quite matching his mild expression. “I can’t allow anyone to go and manhandle him, no matter how you feel.” 

Ritsuka watched, heart in his throat, as Olga Marie’s face twisted into something unreadable and complicated, before she released him, shook off Emiya’s hand and turned around with a disgusted scoff. Emiya rubbed the back of his neck with a laugh and a muttered “This girl…” Ritsuka breathed out in relief, even managing a small smile for the spirit when Emiya glanced down at him; things had become tense, to say the least of the matter, when Emiya had given the ‘basics’ on what it would take for Ritsuka to contract with Caster, even temporarily. He hadn’t given any details on what they’d done, thankfully, but all the same there hadn’t been much question left that something had happened. ‘Intimate contact’ didn’t leave a lot of ambiguity in that regard. 

Mashu was red to the tips of her ears, face half hidden behind her hand, and Dr. Roman was muttering quietly to himself about mana transfer methods, but Olga Marie had gone from shocked to flustered sputtering to angry lightning fast. Even now, as she paced away, she looked even more irritated than she had when he’d come to that first meeting late. Ritsuka wasn’t sure why, exactly, she was so mad when he was the one who had to do things with the servants, and the one who was painfully burning their magical circuits out, and had nearly passed out from the strain on his body. Not that he regretted it, or wanted to stop and let someone else takeover, but he didn’t see why anyone other than him should be upset about any of this. 

It wasn’t like he was backing out because of it. If anything he was pretty sure he’d taken being told he was going to have to have sex with his servants to avoid being in pain pretty well, considering. It wasn’t like he’d asked for this, or wanted them all to be standing around talking about him and Emiya doing...that, or had been goofing off instead of taking this seriously. He was just doing what he had to for the sake of everyone else, because he was the only one who could so it. 

“Se-senpai.” Mashu called quietly. She was looking at him from between her fingers, eyes wide and unblinking. She looked as shell shocked as he’d felt since waking up in this burning city. “Is it...are you...was he gentle with you at least? Is your body okay? Do you need to rest?” 

Ritsuka sputtered and flailed his hands. “W-what? What do you mean by gentle with me? What do you think happened? And why do you think it happened to  _ me _ ?”

Or maybe he didn’t want to know what she thought, if the way she averted her eyes and, impossibly, blushed so hard even her neck became a startling shade of red. Emiya chuckled and, when Ritsuka glared up at him, didn’t even have the grace to look apologetic. Instead he smiled at Mashu; his entire face became softer with the gesture, younger almost. 

“You don’t need to worry, I’ll take good care of our master.” 

This time it was Caster who laughed, hands clasped behind his back as a slightly mocking grin pulled at his lips. “How admirable.” 

If Ritsuka’s face burned any hotter he was positive he was going to manage to burst into flames, or maybe burn out those magical circuits of his despite Emiya’s help. Ritsuka was, suddenly, unsure that death wouldn’t have been a preferable fate to all of *this*. 

“It doesn’t matter!” Olga shouted, casting a bonechilling look over her shoulder at them. “What matters is that you can’t form a contract with Caster so-”

“He can’t?” Caster asked. He was smiling what might have been charmingly, and yet at the same time reminded Ritsuka of the way a thirsty man would look at a glass of water that was just out of reach. A shiver ran up Ritsuka’s spine and his stomach flipped over in uneasy...fear? Anticipation? He wasn’t sure what to call the feeling swimming around in his stomach.  

Olga Marie stiffened for a moment then turned to face then fully, head tilting to the side. Her eyes swept from over Caster from head to toe and back again before sliding over to Ritsuka. “You heard what Archer said? You’ll have to...with  _ him _ .” 

Why did he get the distinct impression he was being insulted?

Caster shrugged. “I don’t have a problem with that, and if my potential master doesn’t find me too unappealing then I don’t see a point in wasting time.” 

All eyes turned to Ritsuka. He was becoming very tired of being the center of attention, something that had rarely happened to him before now. It was funny, he thought as he muttered his agreement, that he would go from easily overlooked to all of this is just a matter of hours. That Caster, who was very much not plain or easily bypassed, was suggesting that he would be the one with a problem here, or find him unappealing… 

Maybe it was a dream. 

“You can’t be serious.” Olga Marie’s eyes jumped from Caster to Ritsuka and back, expression becoming increasingly bewildered. “None of this makes any sense!”   

“You know,”  Roman’s static filled voice filled the air. “It actually makes quite a bit of sense when you think about it. I’d never considered it before but the logic is sound and if Ritsuka consents I don’t see a problem? We aren’t really in a situation to be caught up on the methods we use to fix this singularity.” 

Olga Marie’s mouth dropped open in surprise. It was brief, followed by a sharp inhale and a head shake. “Well! Fine then. You can...go ahead and do what you need to do. I will be over there-“ She pointes off to the side, where a truck had been turned on it’s side and could, perhaps, be used to provide some visual cover. “Don’t take too long. Or be too loud! Mashu, come with me.” 

“W-what? Wait! Senpai, I-” Mashu protested even as Olga Marie grabbed her by the wrist and began to march towards the truck, all but dragging the demi-spirit behind. Distressed was the only way to describe Mashu’s expression as she looked back at Ritsuka for help he didn’t dare offer. Not when it meant antagonizing an already upset and stressed out (understandably so) Olga Marie, and certainly not for the purpose of having Mashu stay behind to watch what was going to happen next. 

It was bad enough that she even knew, and would be so close to potentially overhear or see something. Just the thought made his stomach churn and a cold sweat break out over his suddenly too tight skin. Going from zero sex life, never so much as having been kissed, to being about to do things with a second man in less than two hours, while other people potentially listened was-

Wait. 

“Doctor Roman?” He called, fingers tangling together. “You won’t be listening?” 

“Ah.” The man said, laughing anxiously. “No, I suppose not. I will monitor your body, of course, but there’s no reason for me to listen in.” 

With that the constant low hum that marked the man’s presence, as it were, vanished, leaving true silence in its wake. It was...unnerving, in a way; it had only been a short time but already he was used to having Dr. Roman’s voice in his ear. Ritsuka rubbed at his arms absently, eyes sliding over to where Olga and Mashu were hiding. 

“I suppose you’re staying?” Caster asked, eyes sliding over to Emiya. The archer crossed his arms over his chest and nodded, a frown on his face. Caster smiled again, showing a hint of teeth, but his eyes stayed dark and thoughtful. “Have we met before? I have this feeling that you don’t care for me? Or is it just jealousy over sharing your master?” 

Surprise showed on Emiya’s face for less than a breath before it melted into a wan smile. He shrugged. “Who can say?” 

Ritsuka looked up at Emiya, brow furrowing in confusion; he couldn’t parse that cryptic response, or the breathy laughter it caused in Caster. He felt like he was missing something between the spirits, and the pinched expression on Emiya’s face when Caster sidled up to his side and draped an arm around his shoulders only made it more apparent. Was he really jealous? Ritsuka couldn’t believe that, who would be jealous over *him*, but if it was some other sort of grudge why not just say so? 

Caster’s mouth was right against his ear, breath hot and his voice dark and whiskey smooth when he asked: “Just what did you and your archer do?”  

Ritsuka’s laugh was more nerves than humor. Caster lifted an eyebrow, questioning, and his laughter stopped as abruptly as it had begun. He looked down at his hands, sweat damp and folded together in front of his body, and breathed out slowly, trying to calm his pounding heart. Right, he needed to be serious here. 

Focus. The sooner they began the sooner it could be over and they could get on with their mission, assuming he wouldn’t need to contract with anyone else. ...he hoped he wouldn’t have to contract with anyone else. 

Why had this felt easier with Emiya? Maybe because it had just happened, without much questioning or thought on his part; the spirit had made all the moves and he’d just had to sit there, agree, and let it happen. Having to actually talk about it, make his tongue form the words to answers Caster’s question, was...mortifying. As if response to his embarrassment his mouth became dry and his tongue thick, too heavy to make work, and all he managed was a breathy wheeze. Hardly useful. 

Emiya came to his rescue. Again. He was, it seemed, good at that. “Oral. It’s efficient, and the most we can manage in the circumstances.” 

“The most you could manage.” Caster said lightly, a huff of laughter caressing Ristuka’s ear. “But I’ll leave it there. I suspect your archer wouldn’t allow anything further.” 

The last part was a conspiratorial whisper but Emiya’s snort told Ritsuka it hadn’t gone overheard. It didn’t seem to matter to either spirit though; Caster moved so he was standing in front of Ritsuka, hand sliding from his shoulder to cup his face and Emiya sighed loudly before turning his head away to look elsewhere. It wasn’t even a very good illusion of privacy but it was, Ritsuka supposed, the best he could be getting here. 

Caster’s thumb stroked over his bottom lip, rough and calloused, pale skin and black gloves smelling of grass and pine, as his head was tilted up for Caster to brush a whisper of a kiss to his mouth. Another touch, warm, soft, a chaste pressing of lips for a moment and then firmer, lips slotting together just so. The tip of Caster’s tongue played against the seam of his lips and Ritsuka parted his lips for it with only a second of hesitation. Caster’s other hand curled around the back of his head, long fingers carding through his hair. 

A prickling wave of heat washed over him and some of the tension knotted in his shoulders and back faded away. A stroke of tongue against his own, almost tentative at first before Caster was pulling him closer, fingers curling in his hair and pulling and delving deeper. The kiss turned wet, messy with spit, and loud. Or maybe it was Ritsuka who was becoming loud, his panted breathes and moans he couldn’t help ringing in his own ears. His scalp tingled, but not in a way that was strictly painful; Caster tugged his head back with the fistful he held and Ritsuka’s stomach clenched and his cock twitched and began to harden. 

Ritsuka wouldn’t have guessed kissing people could be so different yet it was not like kissing Emiya at all. This felt...filthy, obscene almost, as drool leaked from the corner of his mouth and their lips smacked together, Caster’s tongue tracing every inch of his mouth like he was committing it to memory. Ritsuka thought absently of the hungry look the spirit had graced him with and knew that he was not being kissed so much as devoured. His knees quaked. 

They parted with a wet pop, gasp, and strings of salvia stretching between them. Ritsuka’s mouth was left alone just long enough for him to suck in a shaky breath before Caster’s thumb was sliding past his swollen, burning lips. The pad pressed against his tongue, pinned it against the bottom of his mouth, slid over the wet muscle, spreading the faint taste of something herbal over it. Ritsuka stared, open mouthed and drooling, up into burning red eyes; his chest constricted, fluttered. The spirit smirked. 

“Mana transfer should work either way we do this, so you’ll have to forgive me for not being as kind as Archer is.” 

Ritsuka blinked, uncomprehending even as Caster’s other hand come down on his shoulder. A light, but insistent push, brought him back to reality a little and spurred him to move with the gesture. His knees hit the ground with Caster’s thumb still hooked into his mouth, over his teeth and against his tongue, keeping Ritsuka’s mouth open. His heart stuttered in his chest. 

He was hard, uncomfortably so in his pants. When had he gotten hard? Why did the way Caster was looking at him, and the feel of his thumb tracing patterns against his tongue, make his dick throb? Why did he feel so strange, head heavy and light all at once, brain wrapped in cotton, skin too tight and burning. 

“Hey, not like that.” Emiya protested from the side, out of Ritsuka’s line of sight. 

Caster’s eyes drifted to the side. “No? Is this a problem, Master?” 

Ritsuka blinked again, head swimming with sluggish thoughts that didn’t seem to want to go anywhere in particular beyond awareness of his own aching need pressing against the back of his zipper and Caster’s finger in his mouth, creeping towards the back of his throat. He could taste the fabric of his glove, feel it drying out his mouth where his spit was seeping into it. 

He shook his head as best he could, and was rewarded with a quick flash of teeth that wasn’t quite a smile from Caster. Electricity zipped down his spine, pooled crackling and alive low in his stomach. Emiya sighed again. 

“Be gentle with him or else.” 

Caster only hummed by way of response. 

Ritsuka stayed where he was, on his knees with his mouth open with, as Caster discarded his hooded cape to fully expose the black sleeveless shirt clinging to his muscular chest, the cloth belts circling his waist were tossed aside carelessly, and the folds of his lower garment loosened and then pushed down his hips. Ritsuka’s eyes followed and then widened. 

He’s seen other guys naked, as a matter of course during gym classes and sports, but never so close or so...erect. Caster’s dick was long, thick, bigger than Ritsuka was all over, and spidered with thick veins along the underside. A slow stroke moved the foreskin back fully, showing a precum slickened head flushed red and a tip starting to ooze a bead of fluid. His eyes traced it down further, to where wiry blue curls surrounded the base and a slight...bulging was starting to form. 

That gave him a moment of pause. The base was reddened, more so than the rest, and the skin was looser but it was distinctly wider there the rest of the shaft was. Was that-

“Alphas are nearly extinct in your time, right?” Caster said, hand sliding down his cock to wrap around the swollen base. That was right; Ritsuka had never even met an alpha in his life let alone imagined he’d be face to crotch with one ever. What was he supposed to do with...that? Caster moved his hand, thumb wet and dripping as he slipped fingers back into Ritsuka’s hair, petting gently. “Don’t trouble yourself with the knot much. Keep your hand around it, tightly, and that will be enough.” 

Ritsuka did as he was told, heart thudding so loudly against his ribcage that he swore he could hear it and wouldn’t have been surprised if the spirits could as well. It was, he decided as he looped his fingers around Caster to mimic the spirit’s hold, not as weird as he would have thought. Hot, really hot, and he could feel it pulsing but other than that it was just firm flesh that yeilded slightly when he squeezed. 

Caster shuddered, lids dropping low and lips parting around a quiet puff of air. “You are a fast learner. Now, come here, mouth open wider and- good. Watch your teeth, I’ll handle the rest.” 

Handling the rest came in the form of guiding Ritsuka down onto his cock, feeding the head past his lips and bumping against his tongue, then rolling his hips forward. The taste of skin, the barest hint of salt and little else, spread over his tongue as warm weight settled over it, rubbed against it as Caster sank deeper into his mouth, and drug back. Ritsuka wasn’t sure what to make of the feeling of having his mouth invaded, made to stretch his lips around the spirit’s cock until he felt a twinge in his jaw, and moved within, but it wasn’t bad so he just shut his eyes and opened up as much as he could to it. 

Another push in, a little further this time, and a push to his head brought Ritsuka closer. Slowly, bit by bit, more of Caster filled his mouth until he could feel the head, slick and blunt, pressed into the back of his throat. 

He gagged then swallowed, trying to acclimate to the feeling. The hand on his head clenched and Caster laughed breathlessly. Ritsuka’s stomach flipped and heat poured into his blood, spread through him, went to his cock and made it strain harder in his pants. “Good. Now try to, mmm, use your tongue. Suck if you can.” 

Ritsuka stayed still for a moment, thinking as his head was moved in Caster’s grasp, trying to recall better what had happened with Emiya earlier. He remembered his mouth mostly, wet and tight, suction and the soft lapping of his tongue. How bright his eyes had been. The hand pumping him in time with the bobbing of Emiya’s head, and how swiftly pressure had built up inside of him. 

He swallowed again, trying to banish some of the spit in his mouth, then pressed his tongue up against Caster’s cock. He ran it along his skin as best he could, feeling every twitch and jump, trying to mimic what he remembered of what Emiya had done. Soft approving moans met his actions and another bloom of warmth went straight to his dick. Caster began to move faster, press in a little further and linger there, holding Ritsuka in place before withdrawing. 

Ritsuka hollowed out his cheeks and sucked, swallowed, forced himself to not cough or choke when it happened. It was hard, his throat jumped and tightened like it wanted to force the tip of Caster’s dick out when it found its way there, but he did his best. Spit trickled out the corner of his mouth, down his chin is sticky streams, and his eyes burned more the longer he let the shape and stretch of Caster’s cock stay in his throat. He squeezed and twisted his hand around the base of the spirit’s dick, a little in awe as he felt it  _ growing _ with each passing moment. 

That meant he was doing a good job, didn’t it? That, and the sounds Caster was making, pleased rumbles and hazy murmurs of what a good job he was doing, what a good master he was sure to be, how pretty he looked. 

Ritsuka reached down, pressed his palm over his own dick then curled his fingers around it as best as he could to rub at himself. It didn’t relieve nearly as much as the pressure he felt building inside as he needed it to but it was something, pleasurable waves that made him moan brokenly and push his hips up against his hand.  

A bitter flavor found his tongue, coated it thick and sticky when the head of Caster’s tongue rubbed down against it. Caster’s hand tightened over the back of his skull, drew him in further then held him perfectly still as he started to buck against him, into his stretched wide mouth, harder. Slurping and wet squelches flooded Ritsuka’s ears, mixed with Caster’s louder panting for breath.

Was he close? A look up found red eyes glazed over, pupils wide, and teeth clamped down on the spirit’s lower lip so tightly all color was being forced from it. It was oddly hypnotic; Ritsuka rolled his hips to rut against his palm harder, faster, and watched Caster’s face like it was the only thing in the world he could see. Caster seemed to realize it, eyes dropping and mouth quirking up; his thumb touched the corner of Ritsuka’s mouth. 

“Let me see what you look like when you come, Master.” 

The words tore through Ritsuka like a lightning strike, lit up his body in a way he couldn’t put words to, crushed him like they had a physical presence and weight. The orgasm he hadn’t realized he was close to hit him, made him shake and whine around the invader in his mouth. He felt wet heat spreading under his palm and for a moment the world grayed around the edges. 

“Good.” Caster murmured. “That’s good.”   

The spirit’s fucked his mouth faster, but with shorter, jerky motions, barely withdrawing from Ritsuka’s mouth at all before pressing back as far as he seemed to dare to go. The knot of flesh under Ritsuka’s now limp grip swelled larger, thrummed under his fingertips. Ritsuka moaned again, cock jumping sticky and spent under his palm, and squeezed weakly at the spirit’s cock. Caster laughed out a curse, head falling back and hand spasming against Ritsuka’s head, and went rigid. Warmth, thick and spurting forth almost violently, hit the back of Ritsuka’s throat and poured down. He wrenched himself back, throat clogged and convulsing, tasted bitter salt for a moment and then his mouth was empty of the spirit’s cock but still full of his release. Another spray, across his nose and, when he turned away from hit, his cheek, hit him as he fell back onto his backside. He lifted a hand, tried to catch what was trying to drip from his mouth before deciding with a grimace he was probably better off swallowing it instead of letting it sit in his mouth. It was thick, hard to get down, and tasted awful but he managed.  

Caster crouched down in front of him, at eye level. The spirit reached out, swiping a hand through the mess dripping from Ritsuka’s face “I’m Cu Chulainn. I’m not much of a Caster, but I’ll do my best for you Master.”    

“Oh.” Ritsuka said, acutely aware of how hoarse his voice was. “...Thank you.” 

**Notes for the Chapter:**

> Next time: The first singularity is handled and, as they reel from the aftermath, Ozy is summoned and he wants a little more than just Ritsuka's mouth for his service. There may be some glimmers of a plot, but it's totally on accidently.


End file.
